Described below is a bus device for a motor vehicle that is designed, as a master bus device, to use a vehicle communication bus of the motor vehicle to exchange messages with slave bus devices. The master bus device is designed particularly for a LIN bus (LIN—Local Interconnect Network). Also described are a corresponding motor vehicle and a method for operating a master bus device on a vehicle communication bus of a motor vehicle.
In a LIN bus, the master bus device sends messages to the remainder of the bus subscribers, that is to say the slave bus devices, in prescribed timeslots and in a prescribed order. The message type is also stipulated. In this case, message type means that a message is sent to a quite particular addressee using a quite particular request. Thus, a message may comprise, by way of example, a control signal to a quite particular slave bus device, such as an activation signal for a sliding roof controller. Alternatively, a message may comprise a request to a slave bus device for it to transmit data of a particular type, that is to say a current temperature, for example. On the basis of the LIN standard, the message in this case comprises the message header, transmitted by the master bus device, with the transmission request, to which message header the slave bus device then appends the requested data.
The specifications pertaining to the transmission times and the message type are obtained from a schedule that is stored in a memory of the master bus device. The schedule is cyclically processed by the master bus device, i.e. following termination of the last step of the schedule the master bus device starts from the beginning again in the schedule. The component of the master bus device that cyclically processes the schedule and exchanges the messages with the slave bus devices is referred to as a transmission device of the master bus device in this case.
The schedule needs to be stipulated and stored in the memory at the time of development of the master bus device. In this case, it needs to take account of all the situations that can arise in a motor vehicle in the course of operation thereof. During normal operation of the motor vehicle, when a driver is using the motor vehicle for travel by it, for example, the master bus device exchanges messages relating to the operation of the motor vehicle with the slave bus devices. If a slave bus device is a sensor, for example, appropriate messages can be used to transmit sensor data from the slave bus device to the master bus device. If the slave bus device is an actuator, that is to say, by way of example, a controller with a motor connected thereto for a sliding roof, for example, the master bus device can use an appropriate message to send a control command for activation.
Besides such messages for normal operation, it must alternatively be possible, for maintenance work, for the master bus device to be able to exchange messages with the slave bus devices for diagnosis or reconfiguration of the slave bus devices. Therefore, the schedule of the master bus device usually has a few timeslots reserved in the schedule for such diagnosis communication with the slave bus device. These timeslots are not used during normal operation, i.e. the master bus device has a respective transmission pause during normal operation of the motor vehicle. Only in the event of maintenance work in a workshop does the master bus device use the timeslot for diagnosis communication.
DE 10 2006 032 217 A1 discloses a method for operating a LIN bus in which an alternative communication protocol is tunneled through the LIN protocol. As a result, LIN messages can each be used to transport sections of a data stream that needs to be transmitted via the vehicle communication bus on the basis of a diagnosis protocol during a diagnosis session.